Fuel cell generator containing a gas sealing means

ABSTRACT

A high temperature solid electrolyte electrochemical generator is made, operating with flowing fuel gas and oxidant gas, the generator having a thermal insulation layer, and a sealing means contacting or contained within the insulation, where the sealing means is effective to control the contact of the various gases utilized in the generator.

GOVERNMENT CONTRACT CLAUSE

The Government of the United States of America has rights in thisinvention pursuant to Contract No. DE-AC-0280-ET-17089, awarded by theUnited States Department of Energy.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to solid electrolyte electrochemical cells, andmore particularly provides a gas confinement scheme for a generatorsystem comprised of such cells.

2. Description of the Prior Art

High temperature solid electrolyte fuel cells convert chemical energyinto direct current electrical energy, typically at temperatures of fromabout 700° C. to 1200° C. This temperature range is required to renderthe solid electrolyte sufficiently conductive for low power losses dueto ohmic heating. With such cells, expensive electrode catalysts andrefined fuels are not required. For example, carbon monoxide-hydrogenfuel mixtures can be used directly, without conversion.

High temperature fuel cell generators employing interconnected, tubularfuel cells, with solid electrolytes, are disclosed by A. O. Isenberg, inU.S. Pat. No. 4,395,468, and by E. V. Somers et al., in U.S. Pat. No.4,374,184. Support tube, fuel electrode, air electrode, solidelectrolyte, and interconnection configurations for individual fuelcells, are disclosed by A. O. Isenberg, in U.S. Pat. No. 4,490,444. Inthe Isenberg fuel cell generator, an exterior metal housing having acontacting, internal thermal insulation layer, usually low densityalumina, surrounds a generating chamber containing a fuel inlet, acombustion product or preheating chamber containing a combustion productoutlet, and an oxidant inlet chamber. The array of individual fuel cellsare contained in the generator chamber.

Yttrium stabilized zirconia is a prime electrolyte candidate for thefuel cells, and is used in a thin layer disposed between an airelectrode and a fuel electrode, all supported on porous ceramic tubularsupport structures. The support tubes for thin film high temperaturesolid oxide electrolyte cells can be made of calcium stabilizedzirconia, and serve as ducts for one of the reactants, fuel or oxidant.Many such fuel cells must be connected electrically in series for highvoltages, since each cell has a terminal voltage of approximately 0.6volt.

Sealing and supporting of such fuel cells has been a concern becausefuel and oxidant reactants must be separated to a large extent, to avoidinteraction other than electrochemical combustion. Additionally, it hasbeen found that water vapor formed in the generating chamber, and alsocarried into the preheating chamber, can carry water through the thermalinsulation layer and condense it on any surfaces whose temperatures arebelow the dew point of the gas mixture in either chamber. Such a "heatpipe" type effect can reduce the insulating effectiveness of theinsulation surrounding all of the chambers. Additionally, any hydrogengas component of the inlet fuel, if permitted to permeate the thermalinsulation in the generating chamber, will reduce the insulation valueby displacing air, since hydrogen has a very high thermal conductivitycompared with air.

What is needed is a gas confinement scheme for the generator system; toseparate the insulation layer from the fuel mixture, and/or to separatethe gases found in the generating and preheating chambers. Such a schemeshould not involve sealing arrangements.

SUMMARY OF THE INVENTION

The disclosed generators eliminate complex seals and allow the oxidantgas, fuel gas, fuel product gas, and an optional insulation gas tocommunicate in a controlled manner. In one concept the oxidant gas, andthe fuel gas, which can contain hydrogen, will be separated by a sealpassing through the porous, gas permeable thermal insulation, extendinginwardly from the exterior housing and positioned at a point between thefuel gas inlet chamber and the combustion product chamber. In anotherconcept the electrochemical generator will have a thermal insulationvolume, containing thermal insulating gas, disposed between an exteriorand interior housing, where the interior housing is disposed between andcan act as a continuous seal between the thermal insulation and allinternal gases and defines an interior volume containing electrochemicalcells. In a third concept an expansion seal is preferably utilized inthe interior housing at a point between the fuel gas inlet chamber andthe combustion product chamber. The generator has associated therewith,means to introduce fuel gas and oxidant gas into the interior volume,and in the second and third concepts, insulating gas into the thermalinsulation, where the insulating gas is maintained at a pressure higherthan the other gases contained within the interior volume.

In preferred form, a gas tight exterior housing having contactinginternal thermal insulation surrounds an interior volume having threechambers which communicate among one another through controlled gasseepage. A fuel gas inlet, or generating chamber, is separated from acombustion product or preheating chamber by a gas porous partition. Thecombustion product chamber is separated from an oxidant gas or an airinlet chamber by a metal sheet.

Tubular solid oxide electrolyte fuel cells are disposed within theinterior housings and preferably extend from the combustion productchamber to the generating chamber. The tubular cells are closed-endedwithin the generating chamber, and open-ended within the combustionproduct chamber. The cells thus pass through and can be partiallysupported by the porous barrier.

Oxidant carrying conduits are loosely supported at one end by the tubesheet, and extend through the combustion product chamber and into theopen ends of the fuel cells. Each conduit corresponds to a single fuelcell and extends through the cell to a point near its closed end. Theconduit includes an open end, or discharge holes, near the closed end ofthe fuel cell, so as to discharge air into the fuel cell.

In the concepts utilizing an interior housing, a gas permeable, porous,internal thermal insulating layer will contain a thermal insulating gas,such as air, nitrogen, or argon, at a pressure P' allowing flow throughthe insulation, and the pressure P' will be greater than the fuel gas,fuel product gas, or oxidant gas pressure P. This air, or inertinsulating gas will preferably be contained within the pore matrix of agas permeable insulating material, such as a refractory, for example,alumina fibers. The internal thermal insulation will be disposed betweenthe exterior housing and the interior housing also surrounding all threechambers. In the third concept, utilizing an expansion seal, there willgenerally be a controlled gas leakage; so that the pressurized, thermalinsulating gas will slowly seep into at least the combustion productchamber at a pressure greater than the fuel gas or reacted fuel productgas, helping to prevent contamination of the insulation. In the conceptswhere the interior housing is used, the flowing thermal insulating gascan sweep away any hydrogen which may have been present in the fuel gasand which may have diffused through the metal interior housing.

In the third concept, utilizing an expansion seal, the interior housingis made up of two adjoining sections which join in the area of the gasporous partition between the fuel gas inlet chamber and the combustionproduct chamber. The seal joint separating the two housing sections canbe an expansion seal joint having a simple trough seal design, whichcompresses a porous, refractory material. This design allows forinterior housing expansion and contraction upon thermal cycling orduring operation of the fuel cell generator, and allows leakage flow ofinsulating gas from the thermal insulation pores into the interiorvolume of the generating chamber. Such controlled leakage of insulatinggas prevents the fuel or reacted fuel product gas from entering andcontacting the thermal insulation layer in the thermal insulationvolume. The third concept can be used when a single piece interiorhousing, or the use of a metal seal through the insulation are notfeasible or desired.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages, nature and additional features of the invention willbecome more apparent from the following description, taken in connectionwith the accompanying drawings, in which:

FIG. 1 is a broken perspective view of one embodiment of a fuel cellgenerator in accordance with one concept of the invention, utilizing aseal through the insulation and not utilizing an interior housing;

FIG. 2 is a broken perspective view of one embodiment of a fuel cellgenerator in accordance with a second concept of the invention,utilizing an interior housing acting as a continuous seal;

FIG. 3 is a broken perspective view of one embodiment of a fuel cellgenerator in accordance with a third concept of the invention, utilizingan expansion seal;

FIG. 4 is a view, partially in section, of a generator such as shown inFIG. 3; and

FIG. 5 is a view, in section, of one embodiment of the expansion sealshown in FIG. 3 and FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in U.S. Pat. No. 4,395,468, herein incorporated by reference, afuel cell arrangement or stack can comprise a plurality of elongatedannular fuel cells. Each fuel cell is preferably tubular and iselectrically connected at least in series to an adjacent cell. Theelectrical connection is made along a selected axial length of thecells, preferably the entire electrochemically active length. Each cellgenerates an open circuit voltage of approximately 0.6 volt, andmultiple cells can be connected in series in order to provide a desiredsystem voltage.

Referring now to FIGS. 1 through 4, there is shown one embodiment of afuel cell generator 10 including an exterior housing 12. While thegenerator is shown in a square configuration in FIGS. 1 through 3, thegenerator and all associated housings can quite advantageously be of acircular or oval cross section. The exterior housing 12 surrounds atleast one chamber, a fuel gas inlet or electrical energy generatingchamber 14, containing a fuel gas, generally containing hydrogen, at apressure P1. An oxidant gas inlet chamber 18, containing an oxidant gasat a pressure P2 can be utilized, as shown in FIGS. 1 through 4. Acombustion product or preheating chamber 16 can also be contained withinthe housing 12. Other means for manifolding an oxidant into conduits 20and then into the generating chamber can also be utilized.

The exterior housing 12 is preferably comprised of 1/32 inch to about1/16 inch thick steel, and lined throughout with an internal thermalinsulation 22, initially containing air as an insulating gas. Thisthermal insulation is disposed as shown between opposite ends of thegenerator. In the concept shown in FIG. 1, where no internal housing isused between the porous thermal insulation 22 and the fuel, combustion,and oxidant gases, said gases, including water vapor will permeate theinsulation. To prevent fuel gas or reacted fuel gas from inlet chamber14 from contacting air or other oxidant, or passing to the otherchambers 16 and 18, except through gas permeable partition 32, a seal 1,which can be a metal sheet inward extension of exterior metal housing12, disposed through the thermal insulation 22 can be used at a pointbetween fuel gas inlet chamber 14 and the other chambers 16 and 18,preferably contacting the porous partition 32 and extending to theexterior housing, as shown.

The concept shown in FIG. 1 could be used in large generators where heatloss through the exterior housing is not as important as simplicity ofdesign. However, in many instances such heat losses are important andthe thermal insulation must be protected from hydrogen gas permeation sothat the insulation will retain its insulating gas within its pores. Onemethod to accomplish this is to provide a continuous interior housingsusceptible to only minor hydrogen permeation at generator operatingtemperatures, to insure the integrity of the thermal insulation.

The continuous internal housing, shown as 13 in FIG. 2, is preferablycomprised of materials resistant to hot contacting gases. Electricalinsulation, to prevent possible shorting of fuel cells to the interiorhousing within the generator chamber, is shown as 15 in FIGS. 2 through4. Penetrating the housings, and insulation, is a fuel inlet means orport 24, shown in FIG. 4, an air inlet means or post 26, and acombustion product outlet means or port 28, as well as ports 57 forelectrical leads 58, shown in FIG. 4. Shown in FIG. 2 are insulating gasentry means or port 5 and insulating gas exit means or port 6. In theconcept of FIG. 2, preferably utilizing a continuous interior housingacting as a continuous seal, any hydrogen that permeates the interiorhousing can be transported or flushed out by the stream of insulatinggas that enters port 5 and exits port 6. The insulating gas will be fedinto entry port 5 at a pressure effective to pass it through the porousthermal insulation, and preferably out the exit port 6. In its progressduring generator operation it can sweep out hydrogen along the way,where the insulating gas is an inert gas, and/or consume i.e., combust,hydrogen where the insulating gas is air. Useful insulation gasesinclude air, nitrogen or an inert gas such as argon, or mixtures thereofand are described in further detail later in the specification. Ports 5and 6 pass through the exterior housing but not the interior housing.

The generating chamber 14, shown in FIGS. 2 through 4, extends betweenan end wall 30 of the housing 12 and a gas porous partition 32. Thepreheating chamber 16 extends between the gas porous partition 32 and asupport structure such as a metal sheet 34. The oxidant inlet chamber 18extends between the sheet 34 and another end wall 36 of the housing 12.The dividing barriers can include other structural types, and additionalsupport and flow baffles can be incorporated. The shown barriers, theporous partition 32 and the sheet 34, need not be sealed structures. Theporous partition 32, in particular, is designed to allow flow betweenthe generating chamber 14, operating at an approximate pressure slightlyabove atmospheric, and the preheating chamber 16, operating at aslightly lower pressure than the generating chamber, as indicated byarrow 38. While the generator 10 is shown in a horizontal orientation inFIGS. 1 through 4, it can be operating in a vertical or other position,and, as mentioned previously, can be of a circular or other design.

High temperature electrochemical cells, such as elongated, solid oxideelectrolyte annular fuel cells 40 are disposed within the generatorinterior volume and extend between the preheating chamber 16 and thegenerating chamber end wall. The cells have open ends 42 in thepreheating chamber 16, and closed ends 44 in the generating chamber 14.The fuel cells are preferably tubular, including a solid oxideelectrolyte sandwiched between two electrodes, preferably supported on atubular porous support. Each cell includes an electrochemically activelength 46 and an inactive length 48. The active length is containedwithin the generating chamber 14. The closed end 44 of the cell iselectrochemically inactive, and can serve for final preheating ofreactant fuel.

Each individual cell generates approximately 0.6 volt, and a pluralityare electrically interconnected, preferably in a series-parallelrectangular array. For descriptive purposes, the arrangement can bedescribed as including rows 50 and columns 52. Each cell in a row 50 iselectrically connected along its active length 46 to the next adjacentcell, preferably through direct contact of their outer peripheries. Forthe preferred configuration shown in FIG. 1, where fuel flows about eachcell and an oxidant, such as air, flows within each cell, the anode isthe outer periphery of each cell and the cathode is on the inside. Thus,cell-to-cell contact within a row is in parallel, among adjacent anodes.Each cell in a column 52 is electrically interconnected in series to thenext adjacent cell 40. In the preferred configuration, thisinterconnection is made from the inner cathode of one cell to the outeranode of the next consecutive cell, through an interconnect 54.

With the configuration described and shown in FIGS. 1 through 4,hundreds of cells can be so connected to achieve the desired voltage andcurrent output. The direct current electrical energy thus generated iscollected by a single current collector, preferably a conductive metalplate 56 or felt pad, positioned in electrical contact with each cell 40in the first row 50', and a similar second collector (not shown),positioned in contact with the last row. Electrical leads 58, shown inFIG. 4, are accordingly provided to the current collectors.

The oxidant conduits 20 are preferably loosely supported at one end inthe sheet 34 as shown best in FIG. 4. The sheet 34 is preferablystainless steel, with bores 60 that fit loosely about the conduits 20 toallow free thermal expansion. The conduits 20 are preferably comprisedof alumina, and the sheet 34 is covered with an insulation 62 such aslow density alumina. A small leakage of oxidant, as indicated by arrow63, is acceptable.

The conduits 20 extend from the sheet 34 into the open end 42 of thefuel cells 40, a single conduit 20 corresponding to a single fuel cell.Each conduit 20 extends to the active length 46 of the fuel cell, andpreferably close to the closed end 44 of the cell, as shown in FIG. 2,the conduit 20 being inserted close to, but spaced from, the closed end44. Radial supports 64 can be utilized to support each conduit 20 withinthe corresponding fuel cell 40. Each conduit can be provided with ameans for discharging a reactant medium into the fuel cell 40, such asopenings 66. The conduits can also be open ended and spaced from the end44 of the fuel cell, or can extend into direct contact with the end 44of the cell, so long as thermal expansion is accommodated.

The gas porous partition 32, which allows a throughput of depleted fuel,is preferably a porous ceramic baffle, such as one comprised of fibrousalumina felt, or ceramic plate segments with porous inserts such asceramic wool plugs, surrounding each fuel cell 40. Small holes 9, shownin FIG. 5, can also be drilled through this partition 32.

According to the third concept of this invention, the interior housingcan consist of two sections and contain a separate seal 70, best shownin FIG. 5. Preferably, this seal will allow for expansion of theinterior housing, yet prevent hydrogen or water vapor entry. However, aseparate, complete hydrogen seal would be very complicated. As analternative, the seal 70 could perform expansion and hydrogen exclusionfunctions, by allowing thermal insulating gas maintained at a pressureP' higher than any other gas within the generator, to seep or leak at acontrolled rate into the interior volume 71 of the generator. The arrowsshown in FIG. 5 indicate probable gas flow. The preferred sealing means70 can be, for example, an expansion joint having the simple trough sealdesign shown most clearly in FIG. 5, where the interior housing 13comprises two sections, 72 and 73.

The seal 70 allows for longitudinal and radial expansion and contractingof sections 72 and 73 upon thermal cycling or during operation of thefuel cell generator. Preferably, section 73, will be made of a materialresistant to hot oxidant gas, such as nickel based alloys with chromiumand iron, for example Inconel 600, containing 76% Ni, 15% Cr and 8% Fe.Preferably, section 72, will be made of a material resistant to hot fuelgas, such as a very high chromium nickel alloy, for example Inconel 601,containing 60.5% Ni, 23% Cr, 14% Fe and 1.35% Al. Both sections will befrom about 1/32 inch to about 1/16 inch thick.

The preferred seal 70 could have, for example, inner lands 74 whichcould compress a flexible winding of alumina fiber sheet 75 into porouspartition 32, as sections 72 and 73 move together due to longitudinaland radial thermal expansion. Additionally the bottom lip 76 of section73 would be forced down into the trough 77 of section 72, which troughcould be filled with fine ceramic powder 78, such as alumina powder, ora packaging of flexible winding of alumina fiber sheet. As shown in FIG.5, minimal insulating or other gas would flow through winding 75. Theinsulating gas would preferentially pass through to the inner land 74contained in preheating chamber 16. Any insulating gas passing throughwinding 75 would be immediately swept through the porous partition 32 orthe opening 9. Any hyrodgen permeating the metal interior housing atoperating temperature of the generator could be consumed, i.e.,combusted, if the insulating gas is air, or if an inert gas is used,hydrogen could be swept through the valve 70 into the interior of thepreheating chamber 16 or swept through the insulation and possibly out atop vent, such as at 81, maintaining the insulating efficiency of thethermal insulation 22.

The gas permeable thermal insulation layer 22, will be from about 2inches to about 8 inches thick, and made of any suitable thermalinsulation having a low thermal conductivity. The thermal insulationwill contain small interconnected voids or pores within the insulationmatrix body capable of containing a gas. The preferred thermalinsulation is a refractory material, such as compacted alumina fibers,preferably from about 1/4 inch to about 3 inches long. The preferredinsulation density is from about 8 lb./cubic foot to about 15 lb./cubicfoot, providing a porosity of from about 60% to about 85%. Naturally themore porous the insulation the more insulating gas it can contain. Theminute voids or pores are designated as 79 in FIG. 5.

The internal, gas permeable thermal insulation 22 is disposed betweenthe interior housing and the gas tight exterior housing, and willcontain a high molecular weight thermal insulating gas having a lowthermal conductivity, i.e. a gas that has a molecular weight of at leastabout 12, preferably a molecular weight between 14 and 85, and that hasan insulating effect substantially greater than hydrogen, for example,preferably, air, nitrogen, or an inert gas such as argon, or mixturesthereof. This gas has over 100 times the insulating effect of therefractory matrix, and it is essential to keep its composition intact.Argon is the most preferred insulating gas, since it would reduce theoxidation rate of outside surfaces of the interior housings.

In the third concept of this invention, utilizing an expansion seal, andillustrated in FIGS. 4 and 5, the thermal insulating gas will bemaintained at a pressure higher than the other gases contained withinthe interior volume near the seal, be they fuel gas, fuel product gas,or oxidant gas, so that thermal insulating gas flows into the interiorvolume of the generator, generally into the combustion preheatingchamber 16, through the seal channel gas leakage means. Preferably, thethermal insulating gas will be at a pressure of at least about 0.05 psi.higher than the pressure of any gases near the seal. A preferredpressure differential to insure controlled leakage of thermal insulatinggas would be from about 0.05 psi to about 0.2 psi higher than thepressure of any gases near the gas leakage means. Pressure differentialsover about 0.2 psi may cause structural deformation of the exterior andinterior housings. This third concept allows insulating gas leakage as ameans of controlling hydrogen and water vapor contamination of thethermal insulation and could be used if the use of a continuous interiorhousing presents fabrication or expansion problems justifying a morecomplicated sealing arrangement. The same pressue range is alsoapplicable to the second concept, where a continuous interior housing isused, i.e., from at least about 0.05 psi to about 0.2 psi higher thanthe gases in the interior volume of the fuel cell generator.

Usually, fuel enters inlet port 24 at a pressure P1 of about 14.9 psi,and oxidant enters inlet port 26 at about 15.1 psi, but due to pressurelosses generally contacts reacted fuel gas at about 14.9 psi. Combustionproduct gases in combustion pre-heat chamber 16 exit outlet 28 at about14.7 psi. In the concept utilizing an expansion seal, the insulatinggas, given such other gas pressures, will be pumped through insulatinggas inlet 80 and optional insulating gas inlet 81, and maintained at apressure P'4 of about 15.15 psi to about 15.3 psi.

The insulating gas inlet 80, and optional insulating gas inlet or topvent outlet 81, shown in FIGS. 3 and 4, provide means for passing thepressurized thermal insulating gas into the pores of the thermalinsulating layer. The ports 80 and 81 pass through the gas tightexterior housing 12, but not through interior housing 13. Inlet 80 willdischarge pressurized insulating gas into the pore volume of theinsulation layer 22. The pressurized insulating gas, which can be fedinto the insulation layer at about 25° C. in all instances where aninterior housing is used, passes through the insulation layer viainterconnected pores and channels and leaks out into the interior volumeof the generator through seal 70, shown in FIGS. 3 through 5, preventingany other gases, including water vapor, near the gas leakage valve fromcontacting or permeating the thermal insulation layer. Thermal expansionof the interior housing will help reduce excess leakage of theinsulating gas into the interior chambers of the generator. When port 81is used as a vent, inert insulating gas such as Argon can be allowed tobleed off with any hydrogen it may be sweeping out.

In FIG. 4, dense zirconia or alumina standoff means 82, shown whichattach interior housing section 73 to the exterior housing 12. Thesestandoffs resist any movement of housing section 73 and help controlthermal expansion and contraction. Nickel alloy compression springs 83,which attach interior housing section 72 to the exterior housing 12 arealso shown. These springs also help control thermal expansion ofinterior housing section 72, and prevent lip 76 from contacting thebottom of trough 77. Both of these expansion control means are optional.The electrical insulation 15 prevents shorting contact and need notcontain insulating gas. These standoffs, springs and electricalinsulation can be used when an interior housing is used.

During operation, an oxidant such as air enters the inlet chamber 18through inlet port 26. The chamber 18 functions as an inlet manifold forthe individual conduits 20. Air enters the conduits at a temperature ofapproximately 500° C. to 700° C., and a pressure above atmospheric,being initially heated prior to entering the housing by conventionalmeans such as a heat exchanger coupled with a blower, not shown. The airflows within the conduits, through the preheating chamber 16, where itis further heated to a temperature of approximately 900° C. The air thenflows through the length of the conduit, being further heated toapproximately 1000° C., and is discharged through the openings 66, shownin FIG. 2, into the fuel cell 40. The air within the fuel cellelectrochemically reacts at the fuel cell cathode along the activelength 46, depleting somewhat in oxygen content as it approaches theopen end 42 of the cell. The depleted air is discharged into thecombustion product or preheating chamber 16.

A fuel, such as hydrogen or a mixture of carbon monoxide with hydrogen,flows from pumping and preheating apparatus, not shown, into thegenerating chamber 14 through fuel inlet port 24, shown in FIG. 2. Thefuel flows over and about the exterior of the fuel cells,electrochemically reacting at the anode. The fuel inlet port 24 ispreferably located near the closed end 44 of the cells 40. The fuelaccordingly depletes as it approaches the porous barrier 32. Thedepleted fuel, containing approximately five percent to fifteen percentof its initial fuel content, diffuses through the barrier 32 and intothe combustion preheating chamber 16.

The combustion product gas, including oxygen depleted air and depletedfuel, along with any air leaking into the preheating chamber 16 throughthe sheet 34, directly react exothermically. The heat of this reaction,which completely combusts the fuel, along with the sensible heat of thedepleted fuel and air, is utilized to preheat the incoming air. Thecombustion products are discharged through combustion product outletport 28 at a temperature of approximateley 700° C. The remaining energyin the combustion products can be utilized to preheat the incoming airor fuel through, for example, an external heat exchanger or to generatesteam in conventional generating apparatus, not shown.

It may also be desirable to preheat the fuel further prior to itscontacting the active length 46 of the fuel cells 40. To acomplish this,the fuel cells 40 can include an enlarged inactive section 76 at thefuel entry end of the housing. The pressure in the preheating chamber 16is lower than that of the generating chamber 14 or oxidant inlet chamber18 in order to assure controlled directional leakage.

A generator in accordance with the arrangement described inself-starting, since fuel is essentially combusted to provide hot,oxidant-rich gases for the cathode. Additionally, preheated fuelprovides the gas for the anode. Also, lean fuel is directly combustedwith oxidant in the combustion product chamber to further preheat theoxidant until a load is applied to the cells, at for example, an activecell temperature of 700° C., Ohmic heating (I² R) in addition to theheat of the electrochemical reaction, including polarization andentropic heat, will bring the generator up to its median operatingtemperature of approximately 1000° C. at the active area.

Electrical contacts to series-parallel connected cells is madepreferably on the fuel side via metal plates, metal rods and felt metalpads. The contacts can be cooled in the feed through point of theexternal housing below the level where metal oxidation is detrimental.

I claim:
 1. A high temperature solid electrolyte electrochemicalgenerator comprising:(A) an exterior housing; (B) a gas permeablethermal insulation layer disposed next to and within the exteriorhousing; (C) an interior volume defined by the thermal insulation, saidvolume containing a fuel gas inlet generating chamber and a combustionproduct chamber containing combustion product outlet means, with a gaspermeable partition dividing said fuel gas inlet generating chamber andcombustion product chamber; (D) a plurality of electrochemical cells,having solid electrolyte, disposed within the generating chamber; (E)means for supplying fuel gas and oxidant gas to the electrochemicalcells for reaction in the generating chamber, so that reacted fuel gaspasses through the gas permeable partition; and (F) seal means disposedthrough the thermal insulation and extending from the exterior housingto the gas permeable partition, so that reacted fuel gas cannot passfrom the generating chamber into the combustion product chamber throughthe thermal insulation, but must pass through the gas permeablepartition into the combustion product chamber.
 2. The electrochemicalgenerator of claim 1, where the seal is a metal sheet seal and theelectrochemical cells are tubular fuel cells, where each fuel cellincludes an electrochemically active length and an inactive length, saidactive length being contained within the generating chamber and saidinactive length passing through the gas permeable partition.
 3. A hightemperature solid electrolyte electrochemical generator comprising:(A)an exterior housing; (B) an interior housing contained within theexterior housing; (C) a plurality of electrochemical cells, having solidelectrolyte, disposed within the interior housing; (D) a gas permeablethermal insulation containing a thermal insulating gas disposed betweenthe exterior housing and the interior housing; and (E) means for passingsaid insulating gas through the thermal insulation.
 4. Theelectrochemical generator of claim 3 also containing means for flowingoxidant gas and hydrogen containing fuel gas to contact theelectrochemical cells and the interior housing, where the interiorhousing is disposed between the thermal insulation and the oxidant gasand the hydrogen containing fuel gas, where said hydrogen in the fuelgas can permeate the interior housing at the operating temperature ofthe generator, and where the thermal insulating gas passing through thethermal insulation is effective to consume and/or sweep away hydrogengas which permeates the interior housing and enters the thermalinsulation.
 5. The electrochemical generator of claim 3, where theinterior housing consists of two sections which are separated by meansof a seal.
 6. The electrochemical generator of claim 3, where theelectrochemical cells are fuel cells, the insulating gas is selectedfrom the group consisting of air, nitrogen, inert gas, and mixturesthereof, and the generator also contains means for collecting currentgenerated by the plurality of electrochemical cells.
 7. A hightemperature solid electrolyte fuel cell generator comprising:(A) anexterior housing; (B) an interior housing contained within the exteriorhousing; (C) a gas permeable thermal insulation layer containing athermal insulating gas having a molecular weight over about 12 disposedbetween the exterior housing and the interior housing; (D) means forpassing said insulating gas into and out of the thermal insulation; (E)an interior volume having a plurality of chambers, including agenerating chamber, defined by the interior housing; (F) a plurality ofelongated fuel cells, having solid electrolyte, each having anelectrochemically active length, disposed within the generating chamber;and (G) means for flowing (1) hydrogen containing fuel gas, capable ofreacting at the fuel cells to form fuel product gas, and (2) oxidant gasinto the generating chamber to contact the fuel cells; where theinterior housing is disposed between the thermal insulation and theoxidant gas and the hydrogen containing fuel gas, where said hydrogen inthe fuel gas can permeate the interior housing at the operatingtemperature of the generator, and where the thermal insulating gaspassing through the thermal insulation is effective to consume and/orsweep away hydrogen which permeates the interior housing and enters thethermal insulation.
 8. The fuel cell generator of claim 7, where theinterior housing consists of two sections which are separated by meansof a seal.
 9. The fuel cell generator of claim 7, where the thermalinsulating gas is selected from the group consisting of air, nitrogen,inert gas, and mixtures thereof.
 10. The fuel cell generator of claim 7,where the thermal insulation layer is a refractory material containinginterconnected pores within the insulation matrix, and the thermalinsulating gas is selected from the group consisting of air, nitrogen,argon, and mixtures thereof.
 11. The fuel cell generator of claim 7,where the thermal insulation layer comprises alumina fibers, and thegenerator also contains means for collecting electrical currentgenerated by the plurality of fuel cells.
 12. A high temperature solidelectrolyte electrochemical generator comprising:(A) an exteriorhousing; (B) an interior housing contained within the exterior housing,said interior housing containing gas permeable seal means and defining afuel gas inlet generating chamber and a combustion product chambercontaining combustion product outlet means, with a gas permeablepartition dividing said fuel gas inlet generating chamber and combustionproduct chamber; (C) a plurality of electrochemical cells, having solidelectrolyte, disposed within the generating chamber; (D) a gas permeablethermal insulation containing a thermal insulating gas disposed betweenthe exterior housing and the interior housing; (E) means for flowingoxidant gas and fuel gas to contact the electrochemical cells; and (F)means for maintaining said insulating gas at a pressure higher than theother gases contained within the interior housing near the gas permeableseal means, so that insulating gas flows into the interior of thegenerator through the gas permeable seal means.
 13. The electrochemicalgenerator of claim 12, where the electrochemical cells are elongatedfuel cells containing solid oxide electrolyte, gases contained withinthe interior housing are prevented from entering the thermal insulationvolume by the flow of thermal insulating gas, the thermal insulating gashas a molecular weight of over about 12, the gas permeable seal means isalso an expansible seal, and the gas permeable seal means separates theinterior housing into two sections at the gas permeable partition, sothat the seal means is disposed next to the gas permeable partition. 14.The electrochemical generator of claim 12, where the thermal insulatinggas is selected from the group consisting of air, nitrogen, inert gas,and mixtures thereof, and where the pressure of the thermal insulatinggas is at least about 0.05 psi higher than the pressure of the othergases near the gas permeable seal means.
 15. The electrochemicalgenerator of claim 12, where the generator also contains means forpassing thermal insulating gas under pressure into the thermalinsulation layer, and where the pressure of the thermal insulating gasis from about 0.05 psi to about 0.2 psi higher than the pressure of theother gases near the gas permeable seal means.
 16. The electrochemicalgenerator of claim 12, where the thermal insulation layer is arefractory material containing interconnected pores within theinsulation matrix, and the thermal insulating gas is selected from thegroup consisting of air, nitrogen, argon, and mixtures thereof.
 17. Theelectrochemical generator of claim 12, where the thermal insulationlayer comprises alumina fibers, and the generator also contains meansfor collecting electrical current generated by the plurality ofelectrochemical cells, and means to pass insulating gas out of thethermal insulation and out of the generator.
 18. The electrochemicalgenerator of claim 12, where the fuel gas contains hydrogen, saidhydrogen can permeate the interior housing at the operating temperatureof the generator, and where the pressurized thermal insulating gas iseffective to consume and/or sweep away hydrogen gas which permeates theinterior housing and enters the thermal insulation.
 19. Theelectrochemical generator of claim 12, where the fuel gas and oxidantgas enter at opposite ends of the generator and where at one end theinterior housing is attached to the exterior housing by means of densestandoffs, and at the other end the interior housing is attached to theexterior housing by means of compression springs, where the standoffsand springs are effective to help control thermal expansion of theinterior housing at the seal means during generator operation.